Microorganisms, such as microalgae and cyanobacteria, may be cultured in a variety of conditions that affect the microorganisms in multiple ways. With each set of culture conditions having unique advantages and disadvantages, a culturing method using a single set of culture conditions may not provide advantages in all the circumstances a culture of microorganisms may experience over the life of the culture. In the prior art, methods of sequentially culturing microalgae in a first phototrophic (or mixotrophic) stage and then a second heterotrophic stage are used to increase accumulation of medium length carbon chain lipids (e.g., C16:0) that are used for biofuel production. The sequential stages of culture conditions attempt to leverage the low cost of phototrophic methods with the high productivity of heterotrophic methods to increase the efficiency of the biofuel production process. While this sequence may be beneficial for the production of lipids used in biofuels, the method is not optimized for the variety of diverse product markets that may be served by microalgae and cyanobacteria through whole biomass, proteins, pigments, polysaccharides, nutritional fatty acids, and others microorganism products.
Beyond lipid production for biofuels, the culture conditions may be more broadly applicable to enhancing the rate of growth, controlling the level of contaminating organisms (e.g., contaminating bacteria, competing organisms, fungi), product formation and accumulation (e.g., proteins, lipids, pigments), and other aspects relevant to the commercial production of microorganisms. Mixotrophic microorganisms provide the capability to culture microorganisms in a more flexible system utilizing a variety of culture conditions for different purposes or for different functions of the microorganisms. Therefore, there is a need in the art for flexible methods of culturing mixotrophic microorganisms in a plurality of culture conditions which optimize the culture for growth and a diverse product profile.